Many recent cameras, and the interchangeable lenses thereof, have an auto focus device (hereinafter referred to as AF) mounted therein, and in such cameras and interchangeable lenses, the focusing operation by the human eye and hand is unnecessary, and this makes such cameras and interchangeable lenses very easy to use, which in turn leads to an increased demand for such cameras with AF.
However, cameras with AF or interchangeable lenses with AF suffer from the disadvantage that the photographer cannot take intentionally out-of-focus photographs even if he or she wants to do it, and in addition, suffers from the disadvantage that the shutter does not operate until the camera or the lens is in focus for an object to be photographed and therefore, the photographer is liable to miss a momentary photographing chance and thus, cameras with AF or interchangeable lenses with AF have been awkward to use to those persons who want to freely use various photographing techniques to take a variety of photographs or those persons who want to seize momentary photographing chances even if the resultant photographs will become more or less out of focus. Therefore, when a photograph which need not be strictly in focus for a particular object to be photographed is to be taken or when an intentionally out-of-focus photograph is to be taken, use has heretofore been made of a conventional interchangeable lens or camera in which focusing s accomplished by only a manual operation. However, in various photographing situations, there arises the necessity of utilizing AF to take in-focus photographs or the necessity of utilizing a manual focus mechanism (hereinafter referred to as MF) to take intentionally out-of-focus photographs. Therefore, it is desirable that both the auto focus operation and the manual focus operation can be accomplished by an interchangeable lens.
With this background, there have been manufactured interchangeable lenses capable of accomplishing both the auto focus operation and the manual focus operation. These conventional interchangeable lenses are designed such that during the auto focus, lens driving is effected by a motor and during the manual focus, a clutch is changed over to thereby manually effect lens driving. Therefore, such interchangeable lenses can accomplish photographing by auto focus and photographing by manual focus and can therefore cope with various photographing situations.
In these conventional interchangeable lenses, however, dog clutch is used to change over the AF and the MF, and this has led to the undesirable possibility that the lens is moved due to a mechanical shock produced during the change-over of the clutch and to the meshing tolerance of the clutch, and in addition, has led to the disadvantage that the operation of changing over the clutch is cumbersome. Also, in the manual focus operation, lens driving is effected manually, and this has led to the problem that the lens driving speed is slow as compared with the auto focus operation and moreover, a considerable operating force is required and this makes such an interchangeable lens awkward to use.
So, to solve the above-noted problems peculiar to such conventional interchangeable lenses, it has been proposed to mount, in the interchangeable lens, a so-called power focus device for driving the lens by a motor during the manual focus operation as well, together with AF, and several propositions have also been made for the power focus device.
The propositions heretofore made for the power focus device include the proposition of using a button switch instead of the conventional focus ring and the proposition of varying the lens driving speed during the manual focus operation by the angle of rotation of a ring-like rotary switch operatively associated with the focus ring (U.S. Pat. No. 4,568,165).
However, in the former proposition, the operating method differs greatly between the button switch and the conventional focus ring and this has led to the disadvantage that the button switch is awkward to use, and in the latter proposition, even if the manual operation is stopped, movement of the lens is not stopped, and to stop the movement of the lens at this time, the rotary switch must be returned to its neutral position. This has led to the disadvantage that the rotary switch is poor in operability and moreover accurate focusing is impossible. Accordingly, it has been difficult to put the power focus device according to the aforementioned two propositions into practical use. Therefore, to make the power focus device practically usable, it is necessary that the manually operated operating member be designed so as to be capable of being operated by just the same operation as the conventional focus ring of MF and that the device for driving the lens be designed such that the movement thereof faithfully follows the movement of the hand.
Also, the applicant proposed Japanese Laid-Open Patent Application No. 196214/1986 (filed on Feb. 26, 1985, Application No. 37240/1985) as an improved proposition relating to the power focus device. The power focus device according to this proposition comprises a motor for driving a focus adjusting lens in response to a drive signal, a control signal generating part for providing the drive direction signal and position control signal of said motor in conformity with the amount of rotation and the direction of rotation of a manually operated rotary switch, a detecting circuit for detecting the drive direction signal and position control signal from said control signal generating part, a signal processing circuit for decoding the detection signal from said detecting circuit and supplying a drive signal to said motor in accordance with said decoding, and a lens information detecting circuit for detecting lens information such as focal length information and stop aperture information and inputting the lens information to said signal processing circuit. An embodiment disclosed in this proposition will hereinafter be described. When the user rotates said rotary switch to the left or right, a pulse signal is output from the contact of said rotary switch in response to said rotational operation. This signal is waveform-shaped by a flip-flop, whereafter it is temporarily memorized by a shift register and is read in at suitable timing by a CPU. On the other hand, the displacement of the signal caused by rotating the operating knob of said rotary switch to the right or left is detected by a phase detector, and the CPU determines the direction of drive of said motor in conformity with the detection signal of the phase detector, and drives said motor in conformity with the read-in signal from said shift register side and in said determined direction. In this manner, said motor is driven in conformity with the direction of rotative operation of said rotary switch and in conformity with the amount of rotative operation of said rotary switch. Consequently, by adjusting the rotated position of said rotary switch, focus adjustment can be accomplished.